U.S. patent application number 12/795000 was filed with the patent office on 2010-11-25 for dye-sensitized photovoltaic cell.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD. Invention is credited to Sung Hen Cho, Sang Hoon Joo, Jin Young Kim, Chang Ho Noh, Chan Ho Pak, Sang Cheol Park, Ki Young Song.
Application Number | 20100294369 12/795000 |
Document ID | / |
Family ID | 38050253 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100294369 |
Kind Code |
A1 |
Kim; Jin Young ; et
al. |
November 25, 2010 |
DYE-SENSITIZED PHOTOVOLTAIC CELL
Abstract
A counter electrode for a photovoltaic cell and a photovoltaic
cell including the same include a transparent substrate and a
catalyst layer formed on the transparent substrate using a
supported catalyst The counter electrode of the present invention
has an economical preparation cost and process, and also has an
enlarged contact area with an electrolyte layer of the cell,
leading to improved catalytic activity. Thus, in the case where the
counter electrode is applied to the photovoltaic cell, excellent
photoconversion efficiency is exhibited. In an exemplary
embodiment, the photovoltaic cell is a dye-sensitized photovoltaic
cell including such a counter electrode.
Inventors: |
Kim; Jin Young; (Suwon-si,
KR) ; Pak; Chan Ho; (Seoul, KR) ; Joo; Sang
Hoon; (Yongin-si, KR) ; Park; Sang Cheol;
(Seoul, KR) ; Cho; Sung Hen; (Seoul, KR) ;
Song; Ki Young; (Seoul, KR) ; Noh; Chang Ho;
(Suwon-si, KR) |
Correspondence
Address: |
CANTOR COLBURN LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD
Suwon-si
KR
|
Family ID: |
38050253 |
Appl. No.: |
12/795000 |
Filed: |
June 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11516386 |
Sep 6, 2006 |
|
|
|
12795000 |
|
|
|
|
Current U.S.
Class: |
136/263 |
Current CPC
Class: |
Y02E 10/542 20130101;
H01G 9/2022 20130101 |
Class at
Publication: |
136/263 |
International
Class: |
H01L 31/0256 20060101
H01L031/0256 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 20, 2006 |
KR |
10-2006-0006313 |
Claims
1. A dye-sensitized photovoltaic cell, comprising: a semiconductor
electrode; an electrolyte layer; and a counter electrode for a
photovoltaic cell, comprising: a transparent substrate; and a
catalyst layer formed on the transparent substrate using a
supported catalyst.
2. The dye-sensitized photovoltaic cell as set forth in claim 1,
wherein the supported catalyst comprises mesoporous carbon; and
metal catalyst particles dispersed and supported in the mesoporous
carbon.
3. The dye-sensitized photovoltaic cell as set forth in claim 2,
wherein the mesoporous carbon has an average mesopore size of about
2 nm to about 20 nm, a surface area of about 500 m.sup.2/g to about
2000 m.sup.2/g and an average primary particle size of about 100 nm
to about 500 nm.
4. The dye-sensitized photovoltaic cell as set forth in claim 2,
wherein the mesoporous carbon has a surface resistance of about 350
m.OMEGA./cm.sup.2 or less under a pressure of 75.4
kg.sub.f/cm.sup.2.
5. The dye-sensitized photovoltaic cell as set forth in claim 2,
wherein the metal catalyst particles have an average particle size
of about 1 nm to about 5 nm and are supported in the supported
catalyst in an amount of 40.about.80 wt % based on a total weight
of the supported catalyst.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. application Ser.
No. 11/516,386, filed on Sep. 6, 2006, which claims priority to
Korean Patent Application No. 10-2006-0006316, filed on Jan. 20,
2006, and all the benefits accruing therefrom under 35 U.S.C.
.sctn.119(a), the contents of which in its entirety are herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates, generally, to a counter
electrode for a photovoltaic cell and a photovoltaic cell including
the same, and more particularly, to a counter electrode for a
photovoltaic cell, which can be prepared through simple and
inexpensive processes using a supported catalyst composed of
mesoporous carbon and metal catalyst particles supported therein,
and to a photovoltaic cell including the same.
[0004] 2. Description of the Related Art
[0005] In light of recent energy problems, thorough research into
replacement energy sources for use instead of conventional fossil
fuel has been conducted. In particular, in order to replace
petroleum resources as an energy source, attempts have been made to
use natural energy, such as wind power, atomic energy, solar
energy, etc., because it is estimated that petroleum resources will
be exhausted within decades.
[0006] Among these natural energy sources, a photovoltaic cell
using solar energy may be unlimitedly employed and is
environmentally friendly, unlike the other energy sources. Thus,
the photovoltaic cell is highly spotlighted as a replacement energy
source. In particular, a dye-sensitized photovoltaic cell has been
researched and is of primary interest due to its very low
fabrication cost.
[0007] Typically, the dye-sensitized photovoltaic cell has a
structure including a semiconductor electrode which absorbs light
to produce and transfer electrons; a counter electrode transferring
electrons, which are returned after having been worked through
external optional circuits, using a redox reaction at the
solid/liquid interface with an electrolyte layer; and the
electrolyte layer positioned between the semiconductor electrode
and the counter electrode and acting as a path transferring ions to
the semiconductor electrode.
[0008] In the photovoltaic cell, the counter electrode is composed
of a conductive transparent substrate and a catalyst layer. Since
the catalyst layer is used to promote the redox reaction, the
activity thereof should be increased.
[0009] The catalyst layer is generally formed by sputtering or
vacuum depositing metal particles having catalytic activity, such
as platinum or palladium, on a transparent substrate. However, when
such metal particles are used alone as the catalyst, a large amount
of the catalyst is used, and expensive vacuum equipment for
sputtering is required. Thus, the preparation thereof is not
efficient or cost-effective. Further, the catalyst layer of the
counter electrode has undesirable low catalytic activity due to the
small reactive surface area of the electrolyte layer. Accordingly,
the diameter of the catalyst particles should be decreased to the
scale of ones of nm (e.g., 1 nm to 9 nm) in order to increase the
reactive surface area and to decrease the usage amount of the
catalyst particles.
[0010] In this regard, U.S. Patent Appl. Pub. No. 2005-0092359
discloses a photovoltaic cell provided with a counter electrode
having a substrate and a conductive carbon layer. In this patent
application, it is intended to increase the reactive surface area,
to decrease the preparation cost and to realize an efficient
preparation process, by forming the catalyst layer contained in the
counter electrode using conductive carbon. However, the disclosure
of this patent application suffers in that, because the counter
electrode is formed using only carbon as a catalyst, it has a
catalytic reactivity much lower than compared to catalysts formed
of metal particles.
[0011] Thus, the development of a novel counter electrode capable
of simultaneously achieving improved catalytic reactivity,
preparation cost-effectiveness, and an efficient preparation
process has become increasingly desired in recent years.
BRIEF SUMMARY OF THE INVENTION
[0012] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the related art, and an aspect
of the present invention is to provide a counter electrode for a
photovoltaic cell, which is economical in terms of preparation cost
and preparation process and has high catalytic activity.
[0013] Another aspect of the present invention is to provide a
dye-sensitized photovoltaic cell that includes the above counter
electrode and thus exhibits excellent photoconversion
efficiency.
[0014] In order to achieve the above aspects, the present invention
provides a counter electrode for a photovoltaic cell including a
transparent substrate and a catalyst layer formed on the
transparent substrate using a supported catalyst.
[0015] As such, the supported catalyst may include mesoporous
carbon and metal catalyst particles dispersed and supported in the
mesoporous carbon.
[0016] In addition, the present invention provides a dye-sensitized
photovoltaic cell comprising a semiconductor electrode, an
electrolyte layer and a counter electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other aspects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0018] FIG. 1 is a graph showing the result of BET surface area
analysis of a mesoporous carbon prepared in Preparative Example 1
in accordance with the present invention;
[0019] FIG. 2 is a sectional side view showing a four point probe
system for measuring sheet resistance of the mesoporous carbon
prepared in Preparative Example 1 in accordance with the present
invention;
[0020] FIG. 3 is a scanning electron micrograph (SEM) showing the
surface of the mesoporous carbon prepared in Preparative Example 1
in accordance with the present invention;
[0021] FIG. 4 is a transmission electron micrograph (TEM) showing
the surface of the supported catalyst prepared in Preparative
Example 4 in accordance with the present invention; and
[0022] FIG. 5 is a graph showing a current-voltage curve of the
photovoltaic cell fabricated in Example 2 in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
exemplary embodiments of the present invention are shown. The
present invention may, however, be embodied in many different forms
and should not be construed as limited to the exemplary embodiments
set forth herein. Rather, these exemplary embodiments are provided
so that this disclosure will be thorough and complete, and will
fully convey the scope of the invention to those skilled in the
art. Like reference numerals refer to like elements throughout.
[0024] It will be understood that when an element is referred to as
being "on" another element, it can be directly on the other element
or intervening elements may be present therebetween. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present. As used herein,
the term "and/or" includes any and all combinations of one or more
of the associated listed items.
[0025] It will be understood that, although the terms first,
second, third etc. may be used herein to describe various elements,
components, regions, layers and/or sections, these elements,
components, regions, layers and/or sections should not be limited
by these terms. These terms are only used to distinguish one
element, component, region, layer or section from another element,
component, region, layer or section. Thus, a first element,
component, region, layer or section discussed below could be termed
a second element, component, region, layer or section without
departing from the teachings of the present invention.
[0026] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," or "includes"
and/or "including" when used in this specification, specify the
presence of stated features, regions, integers, steps, operations,
elements, and/or components, but do not preclude the presence or
addition of one or more other features, regions, integers, steps,
operations, elements, components, and/or groups thereof.
[0027] Spatially relative terms, such as "beneath", "below",
"lower", "above", "upper" and the like, may be used herein for ease
of description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, the
exemplary term "below" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
[0028] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0029] The present invention pertains to a counter electrode for a
photovoltaic cell. The counter electrode includes a transparent
substrate and a catalyst layer formed on the transparent substrate
using a supported catalyst.
[0030] Conventionally, the counter electrode, which is formed by
sputtering or vacuum depositing a metal catalyst itself on a
transparent substrate, suffers because it has a high preparation
cost and a complicated preparation process, and also yields a small
reactive surface area, leading to low catalytic activity, as
discussed above. However, since the counter electrode of the
present invention is formed using a supported catalyst, the above
problems can be eliminated or effectively prevented. That is, in
the present invention, a catalyst for the formation of the catalyst
layer is a supported catalyst in which nano-sized metal catalyst
particles are supported in mesoporous carbon. Hence, even with the
use of a small amount of metal, a counter electrode having a large
surface area can be easily prepared through a room-temperature
solution process. Further, the loading amount of the metal catalyst
particles can be freely controlled according to appropriate
judgment by those skilled in the art, and thus, in particular, the
preparation cost and the preparation process can be improved.
[0031] The supported catalyst used in the preparation of the
counter electrode for the photovoltaic cell of the present
invention is described below.
[0032] In the present invention, any supported catalyst, which is
typically known for use as a supported catalyst, may be used.
Preferably, a supported catalyst that includes mesoporous carbon
and metal catalyst particles dispersed and supported in the
mesoporous carbon may be used. As such, the metal catalyst
particles are dispersed and distributed on the surface of the
mesoporous carbon and in the pores thereof.
[0033] The mesoporous carbon, which is in the form of porous
particles composed substantially of carbon, is a material having
both micropores and mesopores in an appropriate ratio, unlike
conventional amorphous microporous carbon powder having only
micropores. According to the definition of The International Union
of Pure and Applied Chemistry ("IUPAC"), the term `micropore` means
a pore having a diameter of about 2 nm or less, and the term
`mesopore` means a pore having a diameter of about 2 nm to about 50
nm.
[0034] The pores of the mesoporous carbon may be regularly arranged
or not. In exemplary embodiments, the pores of the mesoporous
carbon have a regular arrangement. Further, the micropores are
interconnected through the mesopores, or the mesopores are
interconnected through the micropores, regardless of the type of
arrangement.
[0035] Such mesoporous carbon is characterized by an average
mesopore size, a surface area, an average primary particle size and
a sheet resistance.
[0036] In the present invention, any mesorporous carbon may be used
without particular limitation so long as it is typically known in
the art. Preferably, mesoporous carbon having an average mesopore
size of about 2 nm to about 20 nm may be used. If the average
mesopore size is less than 2 nm, the flow of electrons is poor and
thus the activity of the catalyst is limited. On the other hand, if
the average mesopore size exceeds 20 nm, the catalyst particles
have a tendency to increase the size thereof upon preparation of
the catalyst, undesirably decreasing the efficiency of the
catalyst.
[0037] In addition, mesoporous carbon having a surface area of
about 500 m.sup.2/g to about 2000 m.sup.2/g may be used. If the
surface area is less than 500 m.sup.2/g, it is difficult to
increase the degree of dispersion of the metal particles to be
supported because the surface area is too small. On the other hand,
if the surface area is larger than 2000 m.sup.2/g, excess
micropores are present, and therefore the diffusion properties of
electron or material are deteriorated, leading to decreased
catalytic efficiency.
[0038] In addition, mesoporous carbon having an average primary
particle size of about 100 nm to about 500 nm may be used. If the
average primary particle size is less than 100 nm, the entire
surface area is decreased due to high interparticular cohesion. On
the other hand, if the average primary particle size exceeds 500
nm, the transfer of electrons and material becomes inefficient. In
exemplary embodiments, the average primary particle size falls in
the range of about 250 nm to about 500 nm.
[0039] In addition, mesoporous carbon having a sheet resistance of
350 m.OMEGA./cm.sup.2 or less under a pressure of 75.4
kg.sub.f/cm.sup.2 may be used. Preferably, the mesoporous carbon
has a sheet resistance of 250 m.OMEGA./cm.sup.2 or less. If the
mesoporous carbon has a sheet resistance exceeding 350
m.OMEGA./cm.sup.2 under a pressure of 75.4 kg.sub.f/cm.sup.2, it
undesirably functions to decrease the conductivity of the electrode
and thus is limited in application to the counter electrode of a
photovoltaic cell.
[0040] In the mesoporous carbon prepared using a carbon source,
examples of the carbon source include, but are not limited to,
carbohydrates, including monosaccharides, disaccharides,
polysaccharides, and mixtures thereof; monomers, including furfuryl
alcohol and aniline; gases, including acetylene and propylene; and
phenanthrene. The mesoporous carbon may be used without limitation
so long as it is prepared from a carbon-containing compound that
may be polymerized (below, referred to as `polymerizable
carbon-containing compound`) through various polymerization modes
such as addition polymerization or polycondensation.
[0041] As such, examples of the monosaccharides include, but are
not limited to, glucose, fructose, mannose, galactose, ribose and
xylose, and examples of the disaccharides include, but are not
limited to, sucrose, maltose and lactose. In exemplary embodiments,
phenanthrene is most preferably used as the source of the
mesoporous carbon. Phenanthrene is a compound having the structure
of Formula 1 below, and cannot be replaced with anthracene, which
is a structural isomer thereof.
[0042] Further, mesoporous carbon, prepared using phenanthrene as
the carbon source, is drastically decreased in sheet resistance
(sheet resistance of 250 m.OMEGA./cm2 or less under a pressure of
75.4 kg.sub.f/cm.sup.2) by 30-80% compared to mesoporous carbons
resulting from the use of the other carbon source, without
sacrificing the other properties, and thus can exhibit more
improvement in conductivity.
##STR00001##
[0043] In addition, the mesoporous carbon may be prepared through a
variety of processes for preparing mesoporous carbon known in the
art. Specifically, for example, a carbon precursor mixture, which
includes a polymerizable carbon-containing compound, a solvent, and
a selectively usable acid, is prepared, after which mesoporous
silica, serving as a template, is impregnated with the above
mixture for a predetermined period of time. The resultant product
is heat treated at a predetermined temperature (e.g.,
50.about.250.degree. C.) and heat decomposed and thus carbonized
(e.g., 400.about.1400.degree. C.), and silica is then removed
therefrom using a silica soluble solution (e.g., an aqueous
solution of hydrofluoric acid (HF) or an aqueous solution of sodium
hydroxide (NaOH)), thus preparing a desired mesoporous carbon.
[0044] As such, the amount of each of the components of the
precursor mixture is not particularly limited so long as it does
not inhibit the purpose of the present invention. More
specifically, for example, in the case where phenanthrene is used
as the polymerizable carbon-containing compound, 5.about.15 wt % of
phenanthrene, 10.about.35 wt % acid and 55.about.80 wt % of solvent
may be used. In addition, the mesoporous silica template may be
used without particular limitation so long as it is a molecular
sieve material having a structure in which one-dimensional pores
are interconnected through micropores. Preferably, examples of the
mesoporous silica include MCM-48, SBA-1, SBA-15, KIT-1, MSU-1,
etc.
[0045] Although the metal catalyst particles supported in the
mesoporous carbon are not particularly limited, specific examples
thereof include platinum (Pt), titanium (Ti), vanadium (V),
chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),
copper (Cu), zinc (Zn), aluminum (Al), molybdenum (Mo), selenium
(Se), tin (Sn), ruthenium (Ru), palladium (Pd), tungsten (W),
iridium (Ir), osmium (Os), rhodium (Rh), niobium (Nb), tantalum
(Ta), lead (Pb), bismuth (Bi), or mixtures thereof.
[0046] The metal catalyst may be a single metal or an alloy of two
or more metals. Since the metal catalyst is used in the catalyst
layer of the counter electrode of the photovoltaic cell, the use of
platinum or a platinum alloy is preferable.
[0047] When the average particle size of the metal catalyst
particles is too small, there is a low probability of promoting the
catalyst reaction. On the other hand, when the average particle
size of the metal catalyst particles is too large a decreased
reactive surface area of the catalyst particles results, thus
lowering catalytic activity. Therefore, the average particle size
of the metal catalyst particles is preferably in the range of about
1 nm to about 5 nm.
[0048] As the process of preparing the supported catalyst of the
present invention using the mesoporous carbon and the metal
catalyst particles, a variety of supported catalyst preparation
processes known in the art are used, such as impregnation,
precipitation and a colloidal process. For example, the supported
catalyst may be prepared by impregnating the mesoporous carbon with
the metal catalyst precursor solution and then reducing the metal
catalyst precursor. Such processes are specifically well known in
the literature, and thus are not further described herein.
[0049] In the present invention, the amount of the metal catalyst
particles in the supported catalyst may be freely controlled in the
range of about 1.about.80 wt % depending on appropriate judgment by
those skilled in the art. If the amount of the metal catalyst
particles in the supported catalyst is too small, it is impossible
to apply the catalyst to the photovoltaic cell. On the other hand,
if the amount of metal catalyst particles in the supported catalyst
is too large, economic benefits are negated, and the particle size
of the catalyst may be increased. Thus, the metal catalyst
particles are preferably used in an amount of about 40.about.80 wt
% based on the total weight of the supported catalyst.
[0050] The counter electrode for a photovoltaic cell of the present
invention includes the catalyst layer formed using the supported
catalyst mentioned above. More, specifically, the counter electrode
for a photovoltaic cell of the present invention includes a
transparent substrate and the catalyst layer formed on the
transparent substrate using the supported catalyst.
[0051] In the present invention, the catalyst layer is formed by
uniformly dispersing the supported catalyst in an organic solvent
to prepare a slurry or a paste, which is then applied on the
transparent substrate through a general room-temperature solution
process.
[0052] In this way, since the supported catalyst having the
nano-sized metal catalyst particles supported therein is used, the
counter electrode may be formed through a general room-temperature
solution process, and thus, a high preparation cost is not required
and the preparation process is not complicated.
[0053] As such, a typical organic solvent may be used as the
organic solvent without limitation. Specific examples of the
organic solvent include, for example, acetone, methanol, ethanol,
isopropylalcohol, n-propylalcohol, butylalcohol, dimethylacetamide
("DMAc"), dimethylformamide, dimethylsulfoxide ("DMSO"),
N-methyl-2-pyrrolidone ("NMP"), tetrahydrofuran ("THF"),
tetrabutylacetate, n-butylacetate, m-cresol, toluene,
ethyleneglycol ("EG"), .gamma.-butyrolactone and
hexafluoroisopropanol ("HFIP"), which may be used alone or in
combination with any of the foregoing. Further, specific examples
of the room-temperature solution process include, but are not
limited to, spin coating, spray coating, screen printing, doctor
blading and ink jetting, for example.
[0054] The transparent substrate is not particularly limited so
long as it is transparent. Specifically, a glass substrate or a
plastic substrate may be used. In order to increase the
conductivity, the transparent substrate is preferably coated with
conductive material, such as indium tin oxide ("ITO"), fluorine
doped tin oxide ("FTO"), ZnO--Ga.sub.2O.sub.3,
ZnO--Al.sub.2O.sub.3, SnO.sub.2--Sb.sub.2O.sub.3, etc.
[0055] In addition, the present invention pertains to a
dye-sensitized photovoltaic cell having the exemplary counter
electrode.
[0056] Specifically, the photovoltaic cell of the present invention
is composed of a semiconductor electrode, an electrolyte layer and
the exemplary counter electrode mentioned above.
[0057] The counter electrode of the present invention has a low
preparation cost and a simple preparation process. In addition, the
surface area of the counter electrode in contact with the
electrolyte layer is increased, leading to high catalytic activity.
In the case where such a counter electrode is applied to the
photovoltaic cell, electron transfer performance is improved, and
therefore excellent photoconversion efficiency is realized.
[0058] In the photovoltaic cell, the semiconductor electrode has a
structure that includes a transparent substrate, a semiconductor
layer formed on the transparent substrate and a dye adsorbed on the
surface of the semiconductor layer. The semiconductor electrode may
be formed by applying porous metal oxide on the transparent
substrate and sintering the metal oxide to form a metal oxide film,
which is then impregnated with a dye solution for a predetermined
period of time so as to adsorb the dye on the surface of the metal
oxide film.
[0059] As such, a substrate that is the same as that used in the
counter electrode of the present invention may be used as the
transparent substrate. Although such a metal oxide is not
particularly limited, at least one metal oxide selected from the
group consisting of titanium oxide, niobium oxide, hafnium oxide,
tungsten oxide, tin oxide and zinc oxide may be used.
[0060] The process of applying the metal oxide includes general
coating processes, such as screen printing, spin coating, for
example. The dye may be used without limitation so long as it is
typically used in the field of photovoltaic cells. Specifically,
examples of the dye include ruthenium complex; xanthene dyes, such
as rhodamine B, rose bengal, eosin, or erythrosine; cyanine dyes,
such as quinocyanine, or cryptocyanine; basic dyes, such as
phenosafranine, capri blue, thiosine, or methylene blue; porphyrin
compounds, such as chlorophyll, zinc porphyrin, or magnesium
porphyrin; azo dyes; phthalocyanine compounds; complex compounds,
such as Ru trisbipyridyl; anthraquinone dyes; and polycyclic
quinone dyes, which may be used alone or in combination with any of
the foregoing.
[0061] In addition, the electrolyte layer of the photovoltaic cell
is formed of an electrolyte solution. For example, an acetonitrile
solution of iodine, an NMP solution or 3-methoxypropionitrile may
be used, but the present invention is not limited thereto. Any
material may be used without limitation so long as it has a hole
transport function.
[0062] Moreover, a method of fabricating the dye-sensitized
photovoltaic cell having the above structure of the present
invention is not particularly limited, and any method may be used
without limitation so long as it is known in the art.
[0063] A better understanding of the present invention may be
obtained in light of the following examples, which are set forth to
illustrate, but are not to be construed to limit, the present
invention.
Preparation of Mesoporous Carbon
Preparative Example 1
[0064] 0.9 g of phenanthrene and 2.7 g of para-toluene sulfuric
acid were completely dissolved in 7.5 g of acetone to prepare a
uniform precursor mixture. The precursor mixture was divided into
proportions of 41.0(i): 29.5 (ii): 23.0 (iii): 6.5 (iv), after
which 1 g of SBA-15 was impregnated with the solution (i). The
SBA-15 thus impregnated was dried for 30 minutes in a hood at room
temperature and then further dried at 160.degree. C. for 10
minutes.
[0065] The dried product was further impregnated with the solution
(ii), and then dried as mentioned above. Subsequently, the above
impregnation and drying procedures were repeatedly conducted using
the solutions (iii) and (iv), in that order.
[0066] The dried sample was cooled to room temperature, slowly
heated to 200.degree. C. for 1 hour in a nitrogen atmosphere, and
then allowed to stand for 6 hours. Thereafter, the sample was
slowly heated to 900.degree. C. for 4 hours and then allowed to
stand for 2 hours. A series of processes of adding the product thus
carbonized to a mixture solution comprising HF, water and ethanol,
and then stirring it, was repeated to remove the SBA-15, thereby
preparing mesoporous carbon.
[0067] From the result of BET surface area analysis shown in FIG.
1, the mesoporous carbon thus prepared could be confirmed to have a
surface area of 924 m.sup.2/g and a pore diameter of 5 nm. BET
stands for Brunauer, Emmett, and Teller, the three scientists who
optimized the theory for measuring surface area. The sheet
resistance measured using a four point probe system was found to be
56.7 m.OMEGA./cm.sup.2 under a pressure of 75.4 kg.sub.f/cm.sup.2
and 22.3 m.OMEGA./cm.sup.2 under a pressure of 150.7
kg.sub.f/cm.sup.2. The sheet resistance was measured in a manner
such that 50 mg of the mesoporous carbon 100 was introduced into
the four point probe system shown in FIG. 2, and then respective
pressures of the above two values were applied. The four point
probe system had one pair of electrodes for measuring voltage and
one pair of electrodes for measuring current (totaling 4
electrodes) provided on the bottom of a chamber receiving the
measuring material. The scanning electron micrograph ("SEM") of the
mesoporous carbon 100 is shown in FIG. 3.
Preparative Example 2
[0068] The mesoporous carbon was prepared in the same manner as in
Preparative Example 1, with the exception that 1.5 g of sucrose was
used instead of phenanthrene, and 0.18 g of sulfuric acid was used
as the acid.
Preparative Example 3
[0069] The mesoporous carbon was prepared in the same manner as in
Preparative Example 1, with the exception that the temperature was
increased not to 900.degree. C. but to 1100.degree. C. upon
carbonization.
Preparation of Supported Catalyst
Preparative Example 4
[0070] 0.5 g of the mesoporous carbon prepared in Preparative
Example 1 was introduced into a vinyl bag, after which 0.9616 g of
H.sub.2PtCl.sub.6 was dissolved in 1.5 ml of acetone. This solution
was introduced into the vinyl bag having the mesoporous carbon and
then mixed. The mixture solution was dried in air for 4 hours,
transferred into a crucible, and then dried in an oven at
60.degree. c. for about 12 hours. Subsequently, the crucible was
loaded into an electric furnace in which nitrogen flows, and then
nitrogen was supplied for 10 minutes, after which the flowing gas
was converted into hydrogen. While the temperature was increased
from room temperature to 200.degree. C. and then maintained for 2
hours, the platinum salt supported in the mesoporous carbon was
reduced. After the gas was converted again into nitrogen, the
temperature was increased to 350.degree. C. at a rate of 5.degree.
C./min, maintained for 5 hours, and then slowly decreased to room
temperature. Subsequently, the carbon material was further
impregnated with the solution of 0.9616 g of H.sub.2PtCl.sub.6
dissolved in 1.5 ml of acetone, followed by conducting a reduction
process, thus obtaining a supported catalyst having 60 wt %
platinum supported therein. The transmission electron micrograph
("TEM") of the supported catalyst thus obtained is shown in FIG.
4.
Preparative Example 5
[0071] The supported catalyst was prepared in the same manner as in
Preparative Example 4, with the exception that the mesoporous
carbon obtained in Preparative Example 2 was used.
Preparative Example 6
[0072] The supported catalyst was prepared in the same manner as in
Preparative Example 4, with the exception that the mesoporous
carbon obtained in Preparative Example 3 was used.
Preparation of Counter Electrode
Example 1
[0073] The supported catalyst prepared in Preparative Example 4 was
dispersed in a dispersion of Nafion.TM. 115 (DuPont Corp.) in
isopropylalcohol to prepare a slurry, which was then applied on a
glass substrate coated with fluorine doped tin oxide ("FTO")
through a spray process and thereafter burned at 400.degree. C. for
30 minutes, thus preparing the counter electrode of the present
invention. As such, the applied catalyst had a concentration of 3
mg/cm.sup.2 based on the amount of platinum.
Fabrication of Photovoltaic Cell
Example 2
[0074] A glass substrate was coated with fluorine doped tin oxide
("FTO") by sputtering, further coated with a paste of TiO.sub.2
particles having a particle size of 13 nm by screen printing, and
then burned at 450.degree. C. for 30 minutes, thus forming a porous
TiO.sub.2 film having a thickness of about 15 .mu.m. Subsequently,
the glass substrate having the TiO.sub.2 film formed thereon was
dipped into a solution of 0.3 mM ruthenium dithiocyanate
2,2'-bipyridyl-4,4'-dicarboxylate for 24 hours and then dried to
adsorb the dye on the surface of TiO.sub.2 layer, thus fabricating
a semiconductor electrode.
[0075] Thereafter, the semiconductor electrode as a cathode was
assembled with the counter electrode obtained in Example 1 as an
anode. When both electrodes were assembled, the conductive surfaces
of the anode and cathode were disposed facing into the cell so that
the platinum layer and the light absorbing layer faced each other.
As such, a polymer layer about 40 .mu.m thick of SURLYN.TM. (DuPont
Corp.) was interposed between the anode and cathode, and then the
two electrodes were compressed at about 1.about.3 atm on a heating
plate at about 100.about.140.degree. C. Thereby, the polymer was
attached to the surfaces of the two electrodes by heat and
pressure.
[0076] Subsequently, the space between the two electrodes was
filled with the electrolyte solution through fine holes formed in
the surface of the anode, thus completing the dye-sensitized
photovoltaic cell of the present invention. As the electrolyte
solution, an I.sup.3-/I.sup.- electrolyte solution comprising 0.6 M
1,2-dimethyl-3-octyl-imidazolium iodide, 0.2 M LiI, 0.04 M I.sub.2
and 0.2 M 4-tert-butyl-pyridine ("TBP") dissolved in acetonitrile
was used.
[0077] [Evaluation of Properties of Photovoltaic Cell]
[0078] In order to evaluate the photoconversion efficiency of the
cell fabricated in Example 2, photovoltage and photocurrent were
measured. As a light source, a Xenon lamp (Oriel, 01193) was used,
and the radiation conditions (AM 1.5) of the Xenon lamp were
corrected using a standard photovoltaic cell (Furnhofer Institute
Solare Engeriessysteme, Certificate No. C-ISE369, Type of material:
Mono-Si.sup.+ KG filter). The measured photocurrent-photovoltage
curve is shown in FIG. 5. The short-circuit photocurrent density
(I.sub.sc), open-circuit voltage (V.sub.oc) and fill factor (FF)
calculated from the above curve were substituted into the following
equation for calculating the photoconversion efficiency
(.eta..sub.e). The results are given in Table 1 below.
.eta..sub.e=(V.sub.ocI.sub.seFF)/(P.sub.inc)
[0079] wherein P.sub.inc shows 100 mW/cm.sup.2 (1 sun).
TABLE-US-00001 TABLE 1 Photoconversion I.sub.sc (mA/cm.sup.2)
V.sub.oc (mV) FF (%) Efficiency (%) 4.064 684 63 1.757
[0080] As described hereinbefore, the present invention provides a
counter electrode for a photovoltaic cell using a supported
catalyst. In the present invention, the supported catalyst,
comprising mesoporous carbon and metal catalyst particles supported
therein, is used, and thus, the counter electrode may have an
economical preparation cost and less complicated preparation
process. As well, the area of the counter electrode in contact with
an electrolyte layer is enlarged, leading to high catalytic
activity. Further, there is provided a dye-sensitized photovoltaic
cell having such a counter electrode, thereby exhibiting excellent
photoconversion efficiency.
[0081] Although exemplary embodiments of the present invention have
been disclosed for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the present invention as disclosed in the accompanying
claims.
* * * * *